1. Field of the Invention
The present invention relates to the field of liquid meters and more specifically to oscillating piston type liquid meters. The use of oscillating piston type liquid meters is technique well known to those skilled in the art and is recognized for its precision and reliability.
2. Description of the Prior Art
The main element in these counters is a cylindrical chamber referenced 1 in FIG. 1. This chamber has a side wall 6, a bottom 7 and a cover or lid 8, and encloses a piston 2. A small cylinder 11 is supported by the bottom 7 of the chamber 1 while a small cylinder 12 having the same diameter is borne by the lid 8. These two small cylinders are centered with respect to the axis 26 of the chamber 1. Furthermore, a roller 14 is placed at the center of the small cylinder 11. A fixed partition wall 9 with parallel faces is positioned on the internal side of the side wall 6 of the chamber and extends radially throughout the height of this side wall up to the small cylinders 11, 12. The piston 2 is formed by a cylinder divided, in its median part, by a perforated flat wall 3. The diameter of the piston is substantially smaller than the diameter of the chamber 1. A vertical slot 4 made along one of the generatrices of the piston opens out, at the flat wall 3, into an aperture 5 called a bulb of the piston. The flat wall 3 of the piston is provided with studs 13 at the center of its two faces. One stud is positioned above the flat wall and one stud is positioned below the flat wall. The latter has a diameter greater than the diameter of the stud above the flat wall 3. At the closing of the lid 8 of the chamber, the edges of the two small cylinders 11, 12 meet the flat wall 3 of the piston which is then interposed between the two small cylinders 11, 12 while at the same time staying free in its planar motions. Furthermore, the fixed partition wall 9 fits in between the edges 10 of the slot 4 and inside the piston bulb 5.
Specially shaped ports are made on the bottom 7 of the chamber, on either side of the fixed partition wall 9. When the meter is in operation, the liquid penetrates the chamber through one of the ports called an inflow or intake port 24 and emerges by another port called a outflow or discharge port 25. The space between the outer surface of the piston 2 and the inner surface of the chamber 1 forms two recesses. Similarly, the space between the inner surface of the piston and the outer surface of the small cylinders 11, 12 forms two other recesses. The two recesses that open into the intake port and are called intake recesses. The two recesses that open into the outflow port are called outflow recesses. The liquid to be measured that enters the intake recesses communicates its energy to the piston which moves rotationally, while at the same time shifting a given volume of liquid towards the exterior of the chamber by the outflow port. The piston thus oscillates along the fixed partition in a movement, typical in the technique of oscillating pistons, wherein the axis of the piston describes a circle about the axis of the cylindrical chamber while the edges 10 of the slot, which are commonly known as the lips of the piston, slide along the walls of the fixed partition. The stud placed below the flat wall 3 is guided rotationally along the inner walls of the small cylinder or cylinders 11, 12 and around the roller 14. The rotation of the stud above the flat wall 3 increments an accumulating or totalizing revolution counter.
These prior art meters have a certain number of drawbacks related to imperfect mechanical interaction between the piston and the fixed elements of the chamber.
First of all the precision of the meters is limited by the fact that there is leakage of liquid between the different recesses, especially between the lips of the piston and the fixed partition, but also between, respectively, the lower and upper edges of the piston and the bottom and the lid of the chamber, as well as between the edges of the small cylinders and the flat wall of the piston.
As can be seen in FIG. 2, there is an intermediate position P2 of the piston 2 on the fixed partition wall 9, for which the edges 10 of the slot 4 are both in direct contact with the partition wall. For a position P2 such as this, the clearance is the minimum. However, if the position P2 is to be possible, the spacing between the edges of the slot should be far greater than the thickness of the fixed partition wall 9. This results in a transitory gap through which there is leakage during the different stages of the oscillating motion of the piston.
Furthermore, other leaks are caused by clearances between, respectively, the lower edge 15 and the upper edge 16 of the piston 2 and the bottom 7 and the lid 8 of the chamber. To limit this leakage, the approach proposed in the prior art consists in reducing these clearances. The drawback of this approach is that it sensitizes the meter to the impurities that are often contained in the liquid to be measured.
The same approach used to reduce leakage between the flat wall 3 of the piston and the edges of the small cylinders 11, 12 gives rise to the same drawbacks.
The precision of the meters is furthermore restricted by the existence of friction, especially between the lower and upper edges of the piston and the bottom and the lid of the chamber.
Furthermore, the operation of the meter is relatively noisy, especially when the flow rate of liquid introduced into the meter is great, i.e. when the rotational speed of the piston is high.
In fact, the maximum clearance between the fixed partition wall and the edges 10 of the slot 4 is obtained for the position P1 shown in FIG. 2, for which the fixed partition 9 is entirely engaged within the piston 2. Now, in this position, the piston suddenly changes the side by which it is resting on the partition wall. This change is naturally accompanied by a loud clap.
Furthermore, the friction between the piston and the fixed elements of the chamber is a source of noise. This is especially so with friction between, respectively, the lower and upper edges of the piston and the bottom and the lid of the chamber.
Finally the components of the chamber undergo substantial wear and tear.
Indeed the angular profile of the lips of the piston referenced 10 in FIG. 2 imply contact between said lips and the fixed partition wall 9 along one and the same line, thus constituting a linear wearing-out stress.
Clearly, there are other wearing-out regions, especially at the position where the lower and upper edges of the piston are in contact with the chamber.
The aim of the invention is to make a cylindrical chamber for an oscillating piston type meter that overcomes the above-mentioned problems at low cost.